1. Field of the Invention
This invention relates generally to containers for liquids, and more particularly to methods and apparatus for detection of liquid levels of liquids that have either leaked into space between the outer hull and inner hull of a double-hulled ship or barge or the like or are purposefully pumped into a tank.
2. Description of the Prior Art
Modern tanker ships and barges are being designed and built with space between the outer hull and an inner hull in an effort to avoid puncture of cargo tanks, and thereby avoid leakage of liquid contents from cargo tanks into a waterway as a result of collision damage. Instead of there being a single void space around the entire inner hull, there are partitions so as to divide the space into a plurality of compartments so that, in the event of a puncture of the outer hull, only a compartment space can be flooded while the remaining compartments remain dry. Also, in the event of a leak developing at some point in the wall of the inner hull, such leakage will only enter the compartment between hulls and not leak out into the waterway if the outer hull is not damaged at the site of that compartment.
In order to be sure that there is no leakage into a compartment from either the waterway or a cargo tank inside the vessel, it is desirable to be able to detect the presence of liquid in a compartment. Heretofore, that has not been easy. First of all, the compartments are usually sealed so as to avoid entry of water or other liquid from the top, as from a deck, for example. Therefore, if presence of liquid in such compartment is to be detected, it has been necessary to provide a hole in the deck and insert a pole through the hole to the bottom of the compartment, and then raise the pole to see if there is any liquid on the lower end of the pole. Considering the fact that such compartments may be as deep as twelve feet on a river barge, and much deeper on an ocean tanker, the handling of such a measuring pole is not easy. Also, it is time consuming.
It is an object of the present invention to facilitate determination of the presence and depth of liquid in a normally void space in a shipping vessel.
Furthermore, when filling tanks with expensive or dangerous compounds it is desirable to prevent overflow of the liquid.
Thus it is a further object of the present invention to protect against overfills in tanks by determining when a liquid has reached a predetermined critical level.